Method for vapor phase cracking of oil



E, w. GARD Er AL 1,964,686

Filed April 19, 1929 METHOD FOR VAPOR PHASE CRACKING OF OIL June 26,1934.

l Patented June 26, 1934 UNITED STATES PATENT OFFICE METHOD FOR VAPORPHASE CRACKING F OIL Earle W. Gard, Los Angeles, and Blair G. Aldridge,

Long Beach, Calif., assignors to Union Oil Company of California, LosAngeles, Calif., a corporation of California Application April 19,1,929, Serial No. 356,464

4 Claims. (Cl. 196-61) ,Y high pressure vapor into a cracking coil wherethe vapor is heated to cracking temperatures. Preferably no resistanceis placed to the iiow of vapor except that inherent in the coil itself.that is, no back-pressure is maintained on the vapors lo other than thatdue to the frictional resistance of the passage of the vapor through thecoils and condenser, etc.

1 We have discovered that successful vapor phase cracking depends uponhigh velocity of the vapors through the cracking coils since thisresults in uniform heating and prevents carbon deposition. We have foundit advantageous to generate the vapors at very high pressure and toexpand the vapors into the vapor phase cracking coils. Oil is heated athigh pressure, vapor removed under high pressure from the vaporizer andexpanded through coils where heat is imparted to crack the same.

We have found that in order to prevent excessive coke formation it isdesirable to insure that the oil entering the vapor phase cracking coils'be free as possible of liquid particles. It, therefore, is an object ofthis invention to introduce vapor free of liquid to pass at highvelocity through the vapor phase cracking coils. This is accomplished inone form by heating the oil under pressure and distilling it underpressure with pro- 4vision to remove liquid from the vapor and expandingit through the vapor phase cracking coil.

'35 'lhe back-pressure on the vapor-oil separator may be only thefrictional resistance set up to the f 1 of the vapor through thecracking coils and separating equipment.

i We have found that it is desirable to raise the o vapors to theircracking temperature as rapidly as possible. 'Ihis cracking temperaturemay be several hundred degrees higher than the temperature of the vaporsas they are generated. The expansion of the vapors into and through thecoll causes a drop in temperature which militates against their rapidelevation to the cracking temperature. We have found it advisable tosuperheat the vapors before expansion into the vapor phase crackingcoil.

By generating the vapors by a flashing process the vapors are generatedat a high rate and forced through the cracking coils at a high velocity.

It is therefore an object of this invention to heat oil at relativelyhigh pressure and pass the vapors from the oil so heated at highvelocityv through cracking coils where the vapors are decomposed.

It is another object of this invention to insure the passage of liquidfree vapor through the aforementioned cracking coil where the vapors aredecomposed.

It is a further object of this invention to heat oil at high pressure,expand the heated oil through the vapor cracking coil where the vaporsare decomposed.

It is a further object of this invention to insure the passage of liquidfree vapor through the vapor cracking coils just before mentioned.

It is a further object of this invention to distill oil at relativelyhigh pressure and expand the oil n vapor through vapor cracking coilswhere the vapors are decomposed.

It is a further object of this invention to generate vapors at a highrate so that a high velocity of travel through the cracking coils may beobu tained.

It is a further object of this invention to superheat the vapors beforeexpansion into the vapor phase cracking coil.

Another mode of operation is to heat the oil so at high pressure and toash it into an oil and vapor separator and to pass the vapors throughadditional vapor -phase cracking coils.

The invention will be better understood by reference to the drawingwhich shows schematias cally the preferred form employed for carryingout the process.

Oil contained in tank 1. which may be of the nature of fuel oil, gas oilor kerosene distillate. is

passed through line 2, and pump 3, and split at valves 3a and 5a, partof the oil going through the dephlegmator 4, in heat exchange with thevapors therein, and part going through line 5, as will be hereafterexplained. The oil passing from dephlegmator 4, passes through line l0,and heat exchanger 11, in heat exchange with oil passing from 49 andthrough heat exchanger 74. The oil in line 5. passes through heatexchanger 12,

and `loins with the oil passing from heat exchanger 74, in line 6. Theoil from line 6, passes m0 through surge tank 7, which is controlled byline 13, for the venting of any vapors generated therein. The oil passesthrough line i4, and is pumped under high pressure by pump 17 to coil18. A bypass 15, controlled by valve i6, is provided to permit oil inline 2, to pass directly to the coils 1B. An additional by-pass isprovided to permit oil from line 2, to pass through heat exchanger 62,via lines 8 and 9, to join with the oil in 10. The

oil under high pressure is passed through coil 1B, uo

positioned in furnace 19, heated by 20. "I'he pressure in the coil maybe controlled by valve 21. The heated oil passes into vaporizer 22; 22may have a mist extractor such as tiles 22a, washed with an oil fractionsimilar to the evolved vapors introduced through 22h. The pressure inthe coil 18, and vaporizer 22, is controlled by valves 26, 29a, 23, 35,43a and 21. The vapors issuing from vaporizer 22 via 24 may be passedthrough 25, controlled by valve 26, condenser 27, into container 28.Vaporizer 22, may be heated additionally if desired.

In the process described, however, the vapors pass through line 29, andsuperheater coil 29h, controlled by valve 29a, into coils 30, positionedin furnace 30a, heated by burner 30h. The unvaporized portion invaporizer 22, is passed through fluid control valve 23, via 33, valve35, and line 34, and either through line 38, controlled by valve 39, toafurther cracking furnace for viscosity reduction, or is passed throughcooler 40, via valve 37, inline 36, cooled by cooling fluid introducedat 41, exiting kat 42, and the cooled oil is passed through line 44,where it joins oil in line 45, to storage tank 46. All or part of theoil from 22, may be by-passed through valve 43a and line 43, to beinjected into the heated vapors passing from coils 30. Additionally anoil of a characteristic such as oil similar to that contained in tank 1,may be introduced through line 31, controlled by valve 32. Thecommingled oil and vapors pass through line 47, to heat exchanger 12,and are intrdduced through line 48, into the distillation column 49. Atthe bottom of this tower may be introduced super-heated steam or gas at51, to aid in the stripping of the condensate generated in this tower.The vapors and condensate pass counter-current in 50, condensate isremoved in 72. The vapors issue through throat 52, into rectifyingsection. 'The condensate collected at the bottom of this upper sectionis passed through trap 54, and valve 55, together with additionalcooling fiuid if desired, through 56. The vapors in the upper sectionpass through bubble caps 53, the vapors issuing at the top through 57,downward to the dephlegmator 4; the condensate is trapped oi! at 58, topass into the upper part of rectification column together with theadditional cooling fluid if desired, introduced through line 59,controlled by valve 60. The uncondensed vapors issuing from line 61,pass through heat exchanger 62, cooler 63, pass into look-box 64, andinto tank 65. Part or all of the condensate collecting at the bottom ofthe upper section of the distillation column 49, is withdrawn through66, passes through heat exchanger 11, and is pumped by pump 67, throughline 68, and cooler 69, wherein it is cooled by a cooling iluidintroduced at 70, and withdrawn at 71. The cooled oil is introduced intank l, to be recycled in the process. The unvaporized portion iswithdrawn through 72, and pumped by pump 73, through heat exchanger 74.and line 72, into heat exchanger 75, where it is cooled by cooling uidintroduced at 78, and exited at 77, and is passed via line 45, into tank46.

As o ne example o! this process, the operation on gas oil will bedescribed.

Gas oil is passed through coil 18, as previously described, under from500 to 1500 pounds pressure. Inlthis coil, it may be either merelyheated to a distillation temperature at the pressure to be maintained in22, i. e., to about 700" F., or it may be heated above the distillationtemperature to get some cracking, i. e., to about 800 F. As-

suming the process is operated to merely vaporize the oil in 22, it willbe sufficient that the oil is pumped through coil 18, at such pressureas to maintain in vaporizer 22, a vapor pressure of about 500 to 750pounds, controlled by the pressure valves, as previously described. If,however, cracking is to occur, a pressure of about 1000 to 1500 poundsis maintained in coil 18. However, the preferred amount of cracking issuch that not more than 20% conversion occurs in the coils, it havingbeen found that under those conditions, coils 18, are practicallyuncarbonzed, and in view of the fact that the additional cracking is tooccur in the vapor phase, it is inadvisable to carry this liquid phasecracking in coil 18, beyond a. certain point. The oil passes throughvalve 2i, into vaporizer 22, thevapor pressure in this vaporizer willvary from 300 pounds up to the higher pressure maintained in coil 18,and the temperature of the oil may be from 600 F. upward. However, ithas been found advisable, when operating on a gas oil wherein theconversion is not much higher than 20%, or where there has been noconversion in coil 18, to maintain a pressure of about 500 to 750pounds. Starting up the apparatus, a by-pass is provided to permit thepassage of the vapors through condenser 27, to permit the building up ofpressure in vaporizer 22, and proper temperature in coil 18, about 800F. When the proper conditions have been established, the vapor is thenpassed through coil 29h, where it is superheated enough so that onexpansion into coil 30, via 29a, the vapors are not cooled too low andthe heating to their cracking temperature retarded. For example thevapors are superheated 250 F., i. e., to about 1000 to 1l00 F. Thevapors are then passed through valve 29a. The vapor is thus expandedinto a region of lower pressure since the only pressure on the vapors isthe backpressure of the coils and the resistance of the apparatus.Since, however, the coils may build up a pressure to 150 pounds, thisconstitutes the back-pressure on the vapors. This pressure may beincreased by manipulation of valve 29a, to control the back pressure onthe vaporizer, as shown above. The vapors thus pass through the coil atextremely high velocity. Instead of using a valve at 29a, it ispreferred to use a properly designed orice. This will insure the highestpossible velocity of the vapors through coil 30, where the vapors areheated at high temperature, i. e., from 800 to 1200 F., as is usual invapor phase cracking. In view of the very high velocity oi the vaporsand the. relatively small coils employed in 30, as compared withordinary cracking coils, the cracking temperatures may be adjusted tothe best operating conditions. The heating efiiciency will be atmaximum. This we believe happens due to the fact that the efficiency ofthe heat transfer in this process permits the elevation of the wholevolume of the gas passing through the tubes to substantially the sametemperature. In the present processes, in which the vapors pass throughthe heated tubes at much lower rate, the interior of the gas is at muchlower temperature than the tube surfaces, so that, due to poor heattransfer, the tube must be heated to a much higher temperature to obtainthe average temperature which we can obtain by our process.

While it is preferred to design the length of the coil to give theproper cracking time in the furnace, i. e., by providing the length ofcoil, the cracking time may also be controlled by regulating theback-pressure on the vapor phase cracking coil by means of a valve onthe outlet of the coil (not shown) as will be evident to those skilledin the art.

When the oil has passed from the vapor phase cracking coil, it isimmediately contacted with a stream of oil, as for instance, the oilpassing from 22 or fresh oil from l through line 31. The purpose of thisinjected oil is to partially cool the vapors so that they may undergorectification and also agglomerate any fixed carbon or tars which havebeen generated. in the cracking process. The stirring action in the tube30 is so great that no tar or carbon is deposited in the coils. The heatof the vapors may act additionally to crack the injected oil. The mixedvapor and oil at a temperature of 775 F. pass through an exchanger 12,which acts to partially heat the oil passing through the process,through line 5, to 600 F. and the mixed vapor and oil are introducedinto tower 49 at a temperature of 625 F. This is a combined strippingand fractionating tower functioning in the conventional manner; itsoperation is quite evident from the former description. The tower iscontrolled by the reflux dephlegmator 4, and by the introduction of thecooling oil through 59 and 56, so that the desired end point gasoline isremoved through 61, condensed and collected at 65. Reflux collecting atthe bottom of the rectifying section oir the tower 49 and partiallyWithdrawn through 66, gives up part of its heat at 1l to the incomingcharging stock and is passed through cooler 69, to be recycled throughthe process. This condensate is substantially of the character of thegas oil introduced through line 2. The residue collecting at 72 will bethe cracked residuum consisting of the heavy ends produced in coil 30plus the heavy ends of the injected oil. It is withdrawn through line'72 passed through heat exchanger '74 and 75 and collected in 46.

In an alternative method of operation the oil heated at high pressuresis iiashed into 22, valve 29a being wide open. In other words, the onlyback-pressure on the chamber 22 is the backpressure of the system duetofrictional resistance to the iiow of vapors through 30 and thefractionation apparatus. y

By providing a separator and mist extractor the passage of liquidparticles into the vapor phase cracking coils will be prevented. Theprevention of such introduction of liquid is an irnportant feature ofthis process since it prevents the deposition of carbon caused by thedistillation of the oil at high temperatures.

The flashing of the vapor by the sudden expansion of the oil againstmerely the back-pressure of the system insures high velocities throughthe cracking coils.

The previous example of the operation will apply equally to this case.The oil is heated in the coils 18, to about 500 to 1500 F. depending onthe character of the oil and the amount of conversion. Thus, operatingon fuel oil, the oil may be heated to 600 F. and iiashed, or it may beheated to 800 to 900 F., cracked partially, say to 20% conversion, andthe vapors superheated 200 to 250 F. in coil 29h and expanded.

In operating the above process the rate of generation of vapor is high,that is. much greater than that obtained by ordinary distillation wherethe vapors pass directly through the vapor phase cracking coils. In factthe velocity through the coils may be controlled by the rate ofgeneration oi' the vapors. Thus by heating harder and/or increasing thevelocity of travel of the oil through the primary heating coils 18 therate of vaporization and the velocity oi' travel through the coils 29hand 30 may be controlled. In like manner the sudden expansion of the oilheated at high pressure info the vaporizing drum, as explained above,aids in this effect. It would be desirable to obtain as high-a. rate ofvapor generation as possible. This will be easily controlled by the`operation, as will be understood by those skilled in the art.

In operating on a heavy gas oil or on a fuel oil, the residuum withdrawnfrom 22, will be of the nature of a 10 to 15 Baum road oil. This oil maybe cracked to produce a low viscosity, high gravity cil by a crackingoperation which does not form a part of this invention and will not befurther described.

The above description is not to be taken as limiting my invention, butas merely illustrative of the best manner of carrying it out, and manyvariations may be made thereon as will be recognized by those skilled inthe art.

The invention being described in the appended claims:

I claim:

1. A method of cracking oil which comprises heating oil atsuperatmospheric pressure in an advancing stream to a temperature oi'about 'TOW-900 F., partially releasing the pressure and vaporizing saidoil to separate a vapor substantially free from liquid particles fromthe liquid fraction, superheating said separated vapor to a temperatureof about 1000" F. at substantially the pressure of said vapor separationmaterially reducing said pressure and subsequentlycracking said vaporwhile in the vapor phase at a pressure substantially less than ismaintained in the first heating stage, and quenching the vapor productsleaving the cracking zone with a portion oi' said liquid fraction. i

2. A method of cracking oil which comprises heating oil atsuperatmospheric pressure of the order of 1000 to 1500 pounds per squareinch and at a temperature of about 800-900 F. while in an advancingstream to partially crack said oil in the liquid phase, partiallyreleasing the pressure and vaporizing said oil to separate a. vaporsubstantially free from liquid particles from the liquid fraction,superheating said separated vapor to a temperature oi' about 1000 F. atsubstantially the pressure oi vapor separation,

materially reducing said pressure, and subsequently cracking said vaporwhile in the vapor phase at a pressure substantially less than ismaintained in the first cracking stage, and quenching the vapor productsleaving the cracking zone with a portion of said liquid fraction.

3. A method of cracking oil which comprises heating oil in an advancingstream under superatmospheric pressure of the order of 500 to 1500pounds per square inch and at a temperature of about 700-900 F.,separating a vapor substantially free from liquid particles from saidheated oil at pressures substantially lower than that used in theaforesaid heating, superheating said separated vapor to a temperature ofabout i000" F. at substantially said last mentioned pressure,substantially releasing the pressure on said superheated vapor andcracking said vapor in the vapor phase at said released pressure, and

quenching the vapor products leaving the cracking zone with a portion ofthe liquid fraction obtained in the aforesaid separaion.

4. A method of cracking oil which comprises heating oil atsuperatmospheric pressure of the order of 1000 to 1500 pounds per squareinch and at a temperature of 800-90il l". while in an advancing streamto partially crack said oil in the liquid phase. separating a vaporsubstantially free from liquid particles from said partially cracked oilat pressures substantially lower than that used in the aforesaidheating, superheating said separated vapor to a temperature of about1000 F. at substantially said last mentioned pressure, substantiallyreleasing the pressure on said superheated vapor and cracking said vaporin the vapor phase at said released pressure, and quenching the vaporproducts leaving the cracking zone with a portion of the liquid fractionobtained in the aforesaid separation.

EARIE W. GARD. BLAIR G. ALDRIDGE.

SER'IIFICATE F CRRECBON.

Patent No. i,964,686. June 26, 1934.

, EARLE 'il GARD, iT AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page `3,line 9, for Higziomerate" read to agglomerato or dissolve; and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record oi tliecase in the Patent Office.

Signed and sealed this llth day of September, A. D. i934.

Lesl ie Frazer (Seil) Acting Commissioner of Patents.

at a temperature of 800-90il l". while in an advancing stream topartially crack said oil in the liquid phase. separating a vaporsubstantially free from liquid particles from said partially cracked oilat pressures substantially lower than that used in the aforesaidheating, superheating said separated vapor to a temperature of about1000 F. at substantially said last mentioned pressure, substantiallyreleasing the pressure on said superheated vapor and cracking said vaporin the vapor phase at said released pressure, and quenching the vaporproducts leaving the cracking zone with a portion of the liquid fractionobtained in the aforesaid separation.

EARIE W. GARD. BLAIR G. ALDRIDGE.

SER'IIFICATE F CRRECBON.

Patent No. i,964,686. June 26, 1934.

, EARLE 'il GARD, iT AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page `3,line 9, for Higziomerate" read to agglomerato or dissolve; and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record oi tliecase in the Patent Office.

Signed and sealed this llth day of September, A. D. i934.

Lesl ie Frazer (Seil) Acting Commissioner of Patents.

